In the fabrication of multi-layer ceramic modules and devices, it is traditionally been the case that thick-film silver paste is provided for plating on or plating through the ceramic substrate. Conventional, commercial thick-film silver pastes have the advantage of being co-fireable, i.e., are able to be cured in relatively high temperature ovens, along with the ceramic substrate. Unfortunately, available, commercial co-fireable silver paste metallization materials are not solderable. That is, the materials could not be used as the base upon which subsequent components, for example, diodes, could be soldered to the ceramic substrate. Further, conventional materials had the disadvantage of having poor adhesion to the ceramic substrate. Specifically, the silver paste material tended to flake or peel off of the ceramic substrate under various conditions.
As a response to these limitations, a second class of materials was developed which would tolerate soldering of subsequent components to the ceramic package. Unfortunately, such materials were not co-fireable. Accordingly, the ceramic material would first need to be cured in an oven and subsequently exposed to a second heating regime to deposit the metallization.
Regardless of the type of material chosen, in order to solder on subsequent circuit components, it would be necessary to effect at least one additional manufacturing step. This additional step has the potential of introducing numerous additional manufacturing defects into the device. For example, shrinkage differences for different lots of fired ceramic materials may cause "art work" mismatch between the original material and the second fired material. As a result, a device fabricated according to this two-step process may have higher defect rates. Moreover, the mere addition of a second step adds costs to the manufacturing process.
Accordingly, there exists a need for a metallization material which is co-fireable with most commercially available ceramic materials, and is solderable for attaching components subsequent to the manufacturing of the ceramic substrate. Further, the metallization material should also be adapted to have good adhesion to the outside of the ceramic package, discouraging peeling or flaking off of the deposited material.